1. Field of the Invention
This invention relates to a billet induction heating device for heating a columnar metal billet by electromagnetic induction, which comprises a cylindrical heating coil member, billet holding means for holding a billet at one end face, and billet pushing means for pushing the other end face of the billet, and more particularly to an improvement of the billet induction heating device.
2. Discussion of the Related Art
A metal material which is shaped to obtain a metal member is called "billet". In general, billets are available in the form of cylinders different in diameter. In order to facilitate the shaping of a billet readily, the billet is heated before shaped. For this purpose, an induction heating method is employed. In the induction heating method, the billet is set in a cylindrical winding, and the latter is excited with AC current, so that an electromagnetic induction action occurs with the billet; that is, the cylindrical winding forms a magnetic field to cause current to flow in the billet thereby to generate Joule heat therein, so that the billet is heated by the Joule heat thus generated.
A conventional billet induction heating device is as shown in FIGS. 6 through 8. FIGS. 6(a) and 6(b) are a plan view and a front view, respectively, showing the arrangement of the billet induction heating device. FIGS. 7 and 8 show an electrical circuit and a cooling liquid circuit in the device, respectively.
In FIGS. 6(a) and 6(b), reference numeral 1 designates cylindrical billets; and 2, a heating coil unit. The heating coil unit 2 has a round hole 2' the diameter of which is slightly larger than the outside diameter of the billets 1. A polyphase cylindrical winding, which is cooled with liquid such as water, is wound on the heating coil unit 2. When necessary, the heating coil unit 2 is provided with an over-heating sensor. The poly-phase cylindrical winding should have a cooling means to cool the billet which is at high temperature, and itself. For this purpose, the poly-phase cylindrical winding is generally formed by using a tubular conductor, or a so-called "hollow conductor", so that a cooling liquid is allowed to flow in it. That is, the polyphase cylindrical winding itself forms the cooling means.
Further in FIGS. 6(a) and 6(b), reference numeral 3 designates first reciprocating means including a movable body 3' which is moved in parallel with the axial line of the round hole 2'. In the case where the first reciprocating means is so designed as to be driven by air pressure, the movable body 3' is a piston, and a support 3 supporting the movable body 3' is a piston cylinder. Reference character 4' denotes an arm. One end portion of the arm 4 is coupled to the end of the movable body 3', and the other end portion is connected to billet holding means 4, which is columnar or cylindrical, so that the billet holding means is moved in parallel with the axial line of the round hole 2' as the movable body 3' moves. Reference numeral 5 designates a billet receiving stand having a plurality of conveying rollers on its upper surface for receiving billets heated. Reference numeral 6 designates second reciprocating means which is so designed that a movable body 6' is movable in parallel with the axial line of the round hole 2'. In the case where the second reciprocating means is so designed to be driven, for instance, by air pressure, the movable body 6' is a piston, and a support 6" supporting the movable body 6' is a piston cylinder. Reference character 7' denotes an arm. One end portion of the arm 7' is coupled to the end of the movable body 3', and the other end portion is connected to billet pushing means 7, which is columnar or cylindrical, so that the billet pushing means is moved in parallel with the axial line of the round hole 2' as the movable body 6' moves. Reference numeral 8 designates a billet receiving stand having a V-shaped groove in its upper surface for receiving a billet which is to be heated. The heating coil unit 2, the first reciprocating means 3, the receiving stand 5, the second reciprocating means 6, and the receiving stand 8 are mounted on a frame 25.
In FIG. 7, reference numeral 11 designates a flexible lead for supplying current to the polyphase cylindrical winding of the heating coil unit 2; 12, a phase leading capacitor; 13, a polyphase stepdown transformer; 14, an electromagnetic contactor for controlling the application of current to the heating coil unit 2; and 15, a power fuse for interrupting the supply of current when an electrical circuit including the heating coil unit 2 is, for instance, short-circuited.
In FIG. 8, reference numeral 18 designates flexible hoses for supplying a cooling liquid 17 to the cooling means of the heating coil unit 2; 26, pipes through which the cooling liquid is supplied; 19 and 19', a pair of manual valves for controlling the flow rate of cooling liquid 17 or for stopping the supply of cooling liquid 7 in replacing the heating coil unit 2; 19a and 19a', a pair of normally closed manual valves which are opened in an air blow operation which, in replacing the heating coil unit 2, is operated to remove the cooling liquid 17 from the pipes 26, the flexible holes 18, and the heating coil unit 2.
The conventional billet induction heating device designed as described above operates as follows:
With a billet 1 set in the round hole 2' of the heating coil unit 2, the electromagnetic contactor 14 is operated to supply current to the heating coil unit 2. In general, the current supplied to the heating coil unit 2 is large, several kilo-amperes (kA). In this operation, the billet holding means 4 holds the billet 1 at one end 1a thereby to prevent the latter from being sprung out of the round hole 2' by the movable magnetic field which is formed by the polyphase alternating current, and to maintain the billet at a position which is most suitable for the temperature distribution of the billet. When necessary, the billet holding means may be provided with a temperature sensor to directly detect the temperature of the billet. In this case, it can be detected with high accuracy when the temperature of the billet has reached a predetermined value. As is apparent from the above description, a considerably great electromagnetic force is applied to the heating coil unit 2 and the first reciprocating means. Therefore, it is necessary to rigidly secure the heating coil unit 2 and the first reciprocating means 3 to the frame 25.
When the temperature of the billet 1 reaches the predetermined value, the electromagnetic contactor 14 is opened to suspend the application of current, and the first reciprocating means 3 is operated to extend the movable body 3' outwardly thereby to pull the billet holding means 4 out of the round hole 2. When, under this condition, the movable body 3' is further extended, the arm 4' is turned being guided by a guide (not shown), so that the billet 1 becomes movable to the billet receiving stand 5. At the same time, the second reciprocating means 6 is operated to retract its movable body 6' thereby to cause the billet pushing means 7 to push the other end face 1b of another billet 1, which has been set on the billet receiving stand 8 so as to be heated, so that the billet 1 is inserted into the round hole 2' of the heating coil unit 2. As a result, the billet 1 which has been heated up is pushed out of the round hole 2' and set on the billet receiving stand 5. Thereafter, the movable body 3' is retracted so that the billet holding means 4 holds the billet 1 at one end face 1a; that is, the billet 1 becomes readily for heat treatment. Under this condition, the second reciprocating means operates to place another billet 1 on the billet receiving stand 8. The above-described operations are repeatedly carried out while the cooling liquid 17 is kept supplied to the heating coil unit.
In general, in the case where the diameter of the billet is changed; i.e., where a billet smaller in diameter is heated, the billet induction heating device suffers from the following difficulty: That is, the percentage of the magnetic field which is generated by the cylindrical winding to cross the billet is decreased; that is, the heating efficiency is lowered as much. In order to overcome this difficulty, a billet induction heating device has been proposed which comprises: a plurality of heating coil units the round holes of which are different in diameter; in other words, a plurality of heating coil units different in inside diameter, so that whenever the diameter of a billet to be heated is different from that of the preceding one, one of the heating coil units is selected which is most suitable for it. In the conventional billet induction heating device, replacing the heating coil unit is achieved through the following steps:
(1) The operator waits until the temperature of the heating coil unit to be replaced decreases to room temperature.
(2) The supply of cooling liquid is stopped by operating the manual valves. In this operation, the manual valves at the inlet and outlet of the cooling liquid flow path are closed so that the cooling liquid may not flow out.
(3) An air blow operation is carried out to remove the cooling solution from the cooling means of the heating coil unit and the flexible hoses.
(4) The flexible holes are disconnected from the heating coil unit.
(5) The flexible lead and the lead wire of the over-heating sensor are disconnected from the heating coil unit.
(6) The bolts fastening the heating coil unit to the frame are removed.
(7) The heating coil unit is removed from the frame by lifting it with a hoist or the like.
(8) The heating coil unit thus removed is stored at a predetermined storing place.
(9) Another heating coil unit to be installed is received from the storing place, and is set on the frame by lifting it with a hoist or the like.
(10) The heating coil unit thus set is secured to the frame with the bolts.
(11) The lead wire of the over-heating sensor, and the flexible lead are connected to the heating coil unit thus secured.
(12) The flexible hoses are connected to the heating coil unit.
(13) The manual valves are opened to supply the cooling liquid to the heating coil unit.
As is apparent from the above description, replacing the heating coil unit includes a number of operating steps. Hence, the conventional billet induction heating device involves difficulties or problems that the replacement of the heating coil unit takes a lot of time and labor, and in the replacement, errors may occur with the electrical connection, and the flexible hoses may be insufficiently connected to the heating coil unit, and that it is necessary to provide a place to store a plurality of heating coil units for replacement.